Obesity, which can be defined as a body weight more than 20% above the ideal body weight, is a major health concern in Western societies. It is estimated that about 97 million adults in the United States are overweight or obese. Obesity is the result of a positive energy balance, as a consequence of increased ratio of caloric intake to energy expenditure. Epidemiological studies have shown that increasing degrees of overweight and obesity are important predictors of decreased life expectancy. Obesity causes or exacerbates many health problems, both independently and in association with other diseases. The medical problems associated with obesity, which can be serious and life-threatening, include hypertension; type 2 diabetes mellitus; elevated plasma insulin concentrations; insulin resistance; dyslipidemias; hyperlipidemia; endometrial, breast, prostate and colon cancers; osteoarthritis; respiratory complications, such as obstructive sleep apnea; cholelithiasis; gallstones; arterioscelerosis; heart disease; abnormal heart rhythms; and heart arrythmias (Kopelman, P. G., Nature 404, 635-643 (2000)). Obesity is further associated with premature death and with a significant increase in mortality and morbidity from stroke, myocardial infarction, congestive heart failure, coronary heart disease, and sudden death.
Pro-opiomelanocortin (POMC) derived peptides are known to affect food intake. Several lines of evidence support the notion that the G-protein coupled receptors (GPCRs) of the melanocortin receptor (MC-R) family, several of which are expressed in the brain, are the targets of POMC derived peptides involved in the control of food intake and metabolism. A specific single MC-R that may be targeted for the control of obesity has not yet been identified, although evidence has been presented that MC-4R signalling is important in mediating feed behavior (S. Q. Giraudo et al., “Feeding effects of hypothalamic injection of melanocortin-4 receptor ligands,” Brain Research, 80: 302-306 (1998)).
The prohormone pro-opiomelanocortin (POMC) plays a critical role in the regulations of energy metabolism, and is processed by proteases to produce several peptide hormones, including alpha-melanocyte-stimulating hormone (α-MSH or α-MSH1-13). α-MSH is a major regulator of feeding and body weight homeostasis. Studies have shown that α-MSH1-13 is a critical anorexigenic neuromodulator found in the hypothalamus, which inhibits food intake by binding target neurons expressing melanocortin receptors 3 and 4 (MC3R and MC4R) (see Vaisse et al., J. Clin. Invest., 106, 253-62 (2000); and Williams et al., Am. J. Physiol. Regul. Integr. Comp. Physiol., 289:R2-R3 (2005). MC-3R is expressed in the brain, gut, and placenta and may be involved in the control of food intake and thermogenesis. MC-4R is uniquely expressed in the brain, and its inactivation was shown to cause obesity (A. Kask, et al., “Selective antagonist for the melanocortin-4 receptor (HS014) increases food intake in free-feeding rats,” Biochem. Biophys. Res. Commun., 245: 90-93 (1998)).
The enzyme prolylcarboxypeptidase (PRCP, Lysosomal Pro-X carboxypeptidase, angiotensinase C) is a serine protease that cleaves small, biologically active peptides at carboxyl termini linked to a penultimate proline group. α-MSH is a substrate of PRCP due to its C-terminal amino acid sequence, Pro-Val. Recent studies have shown that PRCP initiates the degradation of α-MSH1-13 into inactive extracellular α-MSH1-12, which is effective in reducing food intake and in regulating neuronal functions via melanocortin receptors. In overnight fasted animals, 2.5 ug of α-MSH1-13 induced a 40% reduction in food intake relative to control animals, however, overnight fasted animals treated with 2.5 ug of α-MSH1-12 did not significantly affect food intake compared to the controls. (Wallingford et al., J. Clinical Investigation, Vol. 119, No. 8, August 2009).
Further it has been shown that PRCP inhibition by small molecule protease inhibitors administered peripherally or centrally decreased food intake in wild type and genetically obese animals. Specifically, both the intracerebroventricular to rats and systemic administration to obese, leptin deficient mice of t-butyl carbamate-prolyl prolinal (BPP), which is an inhibitor of PRCP, resulted in a suppression of overnight food intake (Wallingford et al., J. Clinical Investigation, Vol. 119, No. 8, August 2009).
A recent study also showed that PrCP null mice had elevated hypothalamic levels of α-MSH1-13 and were leaner compared with wild-type controls when fed regular chow, and were also resistant to high fat diet induced obesity. Specifically, on a high fat diet, PrCP gt/gt mice also showed a significant reduction in body weight and a reduction in food intake (Wallingford et al., J. Clinical Investigation, Vol. 119, No. 8, August 2009).
These studies suggest that PRCP inhibitors influence food intake and weight maintenance via melanocortin receptors and the control of active α-MSH1-13 levels, and that targeting PRCP activity with central or peripheral administration of inhibitors can reduce food intake.
WO 2005/115446 discloses the role of prolylcarboxypeptidase inhibitors in weight control, control of body fat and food intake; and specific prolylcarboxypeptidase inhibitors, including t-butyl carbamate (BOC)-prolyl prolinal (BPP), N-benzyloxycarbonyl-prolyl-prolinal, diisopropyl fluorophosphates, PMSF, antipain, leupeptin, corn trypsin and mercuric chloride, useful to treat obesity and obesity related disorders. WO 2005/115446 also discloses the association of PRCP with hypertension, dyslipidemia, diabetes, stroke, gallbladder disease, cardiovascular disease, osteoarthritis, rheumatoid arthritis, hypercholesterolemia, angina, atherosclerosis, sleep apnea, respiratory problems, and cancer.
US 2008-0108080 discloses the utility of small molecule compounds with activity against the gene products encoded by PRCP for use in treating obesity.
WO 2007/140896 discloses the association of human PRCP with cardiovascular diseases, hematological diseases, neurological diseases and cancer based upon tissue distribution of PrCP.
The prolylcarboxypeptidase (PRCP) enzyme is disclosed in EP 1498424 and WO 2004/072265.
The present invention is concerned with novel heteroarylpiperidine compounds as inhibitors of prolylcarboxypeptidase which are useful in the treatment and/or prevention of various conditions and diseases mediated by prolylcarboxypeptidase activity including, but not limited to, abnormal metabolism, obesity, diabetes, metabolic syndrome, obesity and diabetes related disorders, such as hypertension, dyslipidemia, stroke, gallbladder disease, cardiovascular disease, osteoarthritis, rheumatoid arthritis, hypercholesterolemia, stable angina, unstable angina, artherosclerosis, sleep apnea, respiratory problems, cancer, stroke, hematological diseases and neurological diseases.
Weight loss drugs that are currently used to treat obesity have limited efficacy and significant side effects. Studies of the weight loss medications orlistat (Davidson, M. H. et al. (1999) JAMA 281:235-42), dexfenfluramine (Guy Grand, B. et al. (1989) Lancet 2:1142-5), sibutramine (Bray, G. A. et al. (1999) Obes. Res. &:189-98) and phentermine (Douglas, A. et al. (1983) Int. J. Obes. 7:591-5) have demonstrated a limited weight loss of about 5%-10% of body weight for drug compared to placebo. The side effects of these drugs and anti-obesity agents further limit their use. Dexfenfluramine was withdrawn from the market because of suspected heart valvulopathy; orlistat is limited by gastrointestinal side effects; the use of topiramate is limited by central nervous system effects; and the use of sibutramine is limited by its cardiovascular side effects which have led to reports of deaths and its withdrawal from the market in Italy. Obese patients generally respond well to surgical interventions that modify the gastrointestinal tract and limit food intake. However, one out of fifty bariatric surgery patients dies within the first 30 days post surgery, and 4.6% of bariatric surgery patients die within the first year (J. Amer. Med. Assoc., 2005, 294, 1903). Another study indicated that 33% of patients that undergo bariatric surgery have complications that require re-hospitalization within the first 6 months post operation (Medical Care, 2009, 47, 531).
There is a need for a weight loss treatment with enhanced efficacy, increased safety, and fewer undesirable side effects. The instant invention addresses this problem by providing prolylcarboxypeptidase inhibitors useful in the treatment and prevention of obesity, diabetes, and related disorders.